Demand was so strong for the cover crop that seed inventory sold-out last year.

"I conducted my initial research on cover crops and literally had to beg to get on agenda's at crop meetings," recalled University of Wisconsin Extension agent Jim Stute, of Rock County, who has conducted cover crop research for 20 years. "Since the introduction of the improved oilseed radish, the requests to speak are nonstop," he told those attending Lakeshore Technical College's Progressive Operators Seminar on January 27 in Cleveland, Wis.

Even though there isn't much peer-review research on oilseed radishes, the cropping community has been sold on them. Charles Hammer, a crop farmer based out of Beaver Dam, Wis., is one such farmer impressed with the oilseed radishes.

"Last year, we had 400 acres of cover crops on our 2,000-acre operation," says Hammer. "We usually plant them after wheat on 30-inch row spacing. Then, we follow-up with corn in spring."

Seed costs for Tillage radishes, one of the main commercial varieties, run about $3 per pound, notes Hammer. "That is why we drill-seed our radishes at a rate of 3 pounds per acre," says the farmer who uses predominately no-till practices. "If we broadcast the radishes, it may take 10 to 12 pounds of seed per acre which raises our costs."

The radishes grow quite rapidly in the late fall. They grow real well until temperatures get into the low teens for three consecutive nights. "Once they decompose, some of the remaining holes look like gopher holes," says Hammer. "In 2010, we took a backhoe and dug out some tillage radishes to see how far they penetrated the soil. The roots were down 26 inches," he said. "Even with the dry year in 2011, Tillage radishes grew to depths of 18 inches. They were worth the effort," concludes Hammer.

"In spring, we plant corn as close as we can to the holes. The holes provide little resistance for the new corn roots," he notes with examples of the tillage radish holes shown in the photo.

Michigan State's Tim Harrigan, who compared seeding radishes and turnips via manure slurry and traditional seeding methods, offers an alternative planting strategy.

"If you need to haul manure in late summer or early fall, consider adding seed to the manure slurry. It will reduce the number of tillage operations," he says. "In our studies, Daikon radishes had 3.6 tons of biomass per acre in the slurry seeding method compared to 1.2 tons of biomass per acre for traditional seed drilling."

University of Wisconsin's Stute offers these tips for those considering planting radishes:
• Go with an improved variety such as Tillage or GroundHog. They have deeper, thicker roots when compared to unimproved varieties.
• Plant radishes at rates of 200,000 plants per acre.
• A little nitrogen helps the radish roots. However, research has shown that over 90 pounds of N per acre encourages more canopy growth and smaller roots.
• If you plant radishes on highly erodible land (HEL), plant with a fibrous root crop such as oats. Otherwise, the radishes can cause biofurrows and funnel water into channels, causing erosion.
• Radishes have a low carbon-to-nitrogen ratio which means radishes decay rapidly. The rapid decay can smell like natural gas at times.

"Our University of Wisconsin Extension team started a multi-year research project on the radishes last year," says Stute. "Like research done at Michigan State, we have not seen a great bump in nitrogen from the cover crop. However, crop farmers like the biotillage properties of the radish. The radishes break up the subsoil and reduce compaction," he says. "They are quite popular. In fact, the entire seed inventory sold-out in 2011. That was enough seed for an estimated 4 to 6 million acres of radishes."